The present invention relates to the placing of a multiple-speed gearbox included in a drive line for vehicles such as trucks, buses, dumpers, haulers with articulated steering, wheel loaders, and which have at least one driven axle.
Normally, in trucks the engine is placed above the front axle of the vehicle. The multiple-speed gearbox is attached to the engine and the driving power is transmitted via a propeller shaft system to one or several driven rear axles. The engine and the gearbox can together amount up to one quarter of the tare weight of the vehicle. Therefore the placement of the engine and the gearbox between themselves and relative to the rest of the vehicle strongly affects those shares of the tare weight of the vehicle that are carried by the front and rear axles respectively. In future trucks the load on the front axle will tend to increase due to, e.g. supplementary equipment that will be needed to meet future exhaust emission legislation. Increased load on the front axle gives e.g. the following negative consequences:                increased wear on tires of the front wheels, —more difficult to load the vehicle with cargo, since the load on the front axle already is near maximum or over legal or practical load for front axle, —big share of vehicle tare weight on front axle gives low traction and driving ability for driven rear axle (especially in unloaded and partly loaded conditions),        an increased load on the front wheels demands greater tire dimensions, which gives increased steering forces and a decreased steering angle.        
Thus, it would be advantageous to find a way to decrease the load on the front axle of a truck.
In buses it is common to place the engine behind the driven rear axle. In principle this means an inverted placement compared to a truck (as described above). Thus, a big share of the tare weight of the bus will be on the driven rear axle. This gives good traction and driving ability. On the other hand the front axle will get a relatively low load, due to a low share of the tare weight lying on the front wheels. Especially under slippery conditions, this can give problems with the steering ability of the bus.
Thus, it would be an advantage to find a way to decrease the load on the rear axle of a bus of the type mentioned above.
Trucks with the engine and gearbox arranged over the front axle of the vehicle and equipped with a driven rear axle, normally have a propeller shaft system connecting the gearbox output shaft and the driven rear axle. The propeller shaft system allows only a certain amount of difference in angle and in eccentricity between its shaft ends. However, the practically possible differences are even more limited. This is a problem when designing a truck with short wheel base. The reason for this is that the propeller shaft becomes relatively short and the differences in angle relatively big. This gives an undesired limitation of how short the wheelbase of a truck can be. Thus, in this aspect, it would be desirable for a truck designer to get more design space. A known way to compensate for this problem is to arrange the engine and gearbox package in the vehicle with a slight inclination so that the difference in angle between the outgoing shaft of the gearbox and the propeller shaft will decrease and, thus, make it possible to shorten the wheelbase a little bit more. The disadvantage of this is that especially the gearbox, with its rear end, will come closer to the ground, and thus get more exposed to road obstacles.
The engine in a truck, such as described above, needs cooling. Normally a cooler is placed in front of the engine. The engine compartments in modern trucks are very densely packaged. This gives air flow problems in the engine compartment and thus cooling problems for the gearbox, which is placed just behind the hot engine. Therefore a modern truck is often equipped with a special cooling system for the gearbox. This makes the engine compartment even more densely packaged. In some vehicles, such as dumpers, the space conditions in the engine compartments are such that it is not suitable to arrange the cooler in close relation to the engine. This increases the complexity of the cooling problem. It would thus be advantageous to be able to get more free space in the engine compartment.
Heavy vehicles have legal and customer requirements on noise emissions. The engine and the gearbox are two components that largely contribute to the sound emission from the vehicle. The development of gearboxes has lately gone towards lower sound emissions from engaging teeth in the gearbox. Unfortunately, this is counteracted by that the vibration level from the engines tends to increase due to, amongst other things, different development steps taken for dealing with the demands coming from new exhaust emission legislation. Since the gearbox normally is attached to the engine, the vibrations from the engine are spread to the gearbox, and the gearbox becomes sort of a loudspeaker that emits vibrations from the engine as sound (noise) to the surroundings. It would be advantageous to be able to decrease the sound emission from heavy vehicles.
Volkswagen type 1 and Porsche 911 both have an engine-gearbox package arranged over the rear driven axle. The engine, gearbox and rear axle are built together as one package. The package is arranged so that most of the engine is behind the rear axle and the gearbox is in front of the rear axle. Porsche 914 and Porsche Boxter also have the engine, gearbox and rear axle built together, but instead here the engine is arranged in front of the rear axle and the gearbox behind the rear axle. Audi 100 has the same concept applied on a driven front axle, i.e. the package is arranged over the front axle. Citroen Traction Avante and Renault 4 are examples on how to apply the Volkswagen type 1 package concept on a driven front axle. The concept of building engine, gearbox and driven axle together in one package works well for cars, but when applied on heavy vehicles, such as e.g. trucks, it would be unpractical and unflexible to try to arrange a big truck engine-gearbox over a driven rear axle and at the same time make room for an efficient load carrier. There would be similar problems for dumpers and buses.
SE521643 shows a power train comprising, amongst other components, an engine, a main gearbox and a range gearbox. The engine and main gearbox are built together and arranged over the undriven front axle. The range gearbox is arranged just in front of the driven rear axle. The front axle load problem (see above) and the sound emission problem (see above) are not improved satisfactory. The cooling problem and the problem with the difference in angle and eccentricity between propeller shaft ends in trucks with short wheelbase (see above) also remain with this solution.
Pontiac Tempest, Porsche 924, 928, 944 and 968, Alfa Romeo Alfetta and Giulietta, and Volvo 300-series all have the engine in the vicinity of the front axle and the gearbox built together with the driven rear axle. The gearbox is placed in front of the rear axle. The problem with load on the front axle is decreased, but for heavy vehicles and driven bogie there is still a need for improvement. Further, there is no suggestion how to solve the cooling problem in densely packaged engine compartments nor how to solve the problem with the difference in angle and in eccentricity between drive shaft ends in trucks with short wheelbase (see above).
Trucks, especially heavy trucks, have parking brakes both for front wheels and rear wheels. This means an increased number of components in the vehicle. If a truck is empty, i.e. the load over the rear axle is low and the load over the front axle is relatively high (due to cab, engine, gearbox and other components arranged in the front and over the front axle of the vehicle), then to be sure having enough brake effect from the parking brake in all situations, the vehicle will need a parking brake both on the front and the rear axle.
It is desirable to decrease the axle load on the axle that has the engine in its vicinity and at the same time increase drivability, steering ability (for bus as above), the possibility of designing trucks with short wheelbase and the cooling performance of the engine. It is also desirable to eliminate the need of a parking brake (for trucks as above) on both front and rear wheels and at the same time to eliminate the need of a special gearbox cooling system. It is also desirable to decrease the sound emission from the vehicle. It is also desirable to, in a truck of the type mentioned above, decrease steering forces and increase steering angle.
The arrangement according to an aspect of the invention comprises a vehicle with wheels arranged on a front axle and rear axle, where at least one of said axles is driven, an engine arranged in the vicinity of rear or front end of said vehicle, said engine comprising an output shaft connected to said driven axle via a transmission system for transmitting driving power from said engine to said driven axle, said transmission system comprising at least a multiple-speed gearbox for causing variable gear ratio between said engine and driven axle. The engine and said gearbox are arranged on each side of said driven axle, and are connected only via a power transmitting device so that an engine block of said engine is separated from a gearbox housing of said gearbox.
A major advantage of the arrangement according to an aspect of the invention for the types of vehicles mentioned is that a better weight distribution is achieved. For trucks of the type mentioned above this results in reduced steering forces and a possibility to achieve a better steering angle, since a smaller tire dimension can be chosen. Correspondingly, for a bus of the type mentioned above this gives a better steering ability. Further, a simpler and cheaper bedding of engine in rubber cushions can be chosen, since only the weight of the engine is left to be taken care of. Special cooling for the gearbox will not be needed. Since the engine and the gearbox are separated, an overall noise reduction for the vehicle will be possible. In a special bogie embodiment with the gearbox placed between the axles the noise reduction would be even better, since the increased number of wheels will work like a sound screen. With the gearbox separated from the engine, there will be more space in the engine compartment and, thus, a better air flow around the engine and the cooler of the engine can be achieved. This gives the possibility to increase the performance of the cooling system and in the extension also the performance of the engine. For the case with a truck having an engine placed above the front axle and having rear wheel drive (see above), the decreased load on the front axle gives decreased wear on tires of the front wheels, makes it easier to load the vehicle with cargo (since the load on the front axle is not near maximum allowable load for front axle), and the better weight distribution gives the vehicle a better traction and driving ability for driven rear axle.
According to an advantageous first embodiment of the arrangement according to an aspect of the invention, said power transmitting device is a propeller shaft where one end of the propeller shaft is connected directly or indirectly to an input shaft of said gearbox. In this embodiment said input shaft is placed higher relative to the ground than the rotational axis of a driven wheel differential gearing of said driven axle and an output shaft of said gearbox is connected to said differential gearing. In a further development of this embodiment the output shaft of said engine, the input shaft and the propeller shaft are placed on mainly the same level relative to the ground and simultaneously higher relative to the ground than said rotational axis of said driven wheel differential gearing. The advantage is that this embodiment gives a truck designer the possibility of designing trucks with even shorter wheelbase than would normally be possible with known technique. The engine would not need to be arranged with a slight inclination, because there is no difference in angle and in eccentricity between the shaft ends of the propeller shaft, to compensate for.
Thus, the engine and the gearbox would be more protected from hitting ground obstacles. The vehicle will get a possibility for better ground clearance without increasing the total height of the truck.
According to an advantageous second embodiment of the arrangement according to an aspect of the invention, said power transmitting device comprises a first hydraulic motor/pump arranged on the engine side of said driven axle and a second hydraulic motor/pump arranged on the gearbox side of said driven axle, said first and second hydraulic motor/pump being connected via hydraulic hoses. The advantage of this is a much increased flexibility in e.g. truck architecture, e.g. by using the space between the engine and the rear axle for batteries, other equipment or cargo. In a special embodiment the hydraulic motor/pump can be arranged in a trailer, which is attached to said vehicle. The advantage is increased traction and driveability.
According to an advantageous third embodiment of the arrangement according to an aspect of the invention, said power transmitting device comprises a first electric motor/generator arranged on the engine side of said driven axle and a second electric motor/generator arranged on the gearbox side of said driven axle, said first and second electric motor/generator being connected through electric wires. The advantage of this is a much increased flexibility in e.g. truck architecture, e.g. by using the space between the engine and the rear axle for batteries, other equipment or cargo. In a special embodiment the electric motor/generator can be arranged in a trailer, which is attached to said vehicle. The advantage is increased traction and driveability.
In a further advantageous fourth embodiment said gearbox is relatively fixed to a frame of said vehicle. Thus, said gearbox is not movable vertically together with a suspension system of said driven wheels. In a further development of this embodiment said driven axle comprises differential gearing and bevel gear. According to an aspect of the invention said gearbox, differential gearing and bevel gear are attached directly to a frame of the vehicle. The gearbox, differential gearing and bevel gear are further not movable vertically in a suspension system together with said driven wheels. Both mentioned embodiments gives a compact and light axle installation with individual wheel suspension.
According to an advantageous fifth embodiment of the arrangement according to an aspect of the invention, said gearbox, differential gearing and bevel gear are integrated and arranged in a common unit. The advantage is a compact build up. In a further development of this embodiment a lubrication system is arranged in said unit for lubricating said gearbox, differential gearing and bevel gear. A lubrication system common for the gearbox, the differential gearing as well as the bevel gear can be used. In an embodiment with driven bogie axels one lubrication system can be used for all the mentioned components, i.e. also for the respective differential gearing of the respective driven axle. An aspect of the invention according to this embodiment is of coarse also applicable if there is only one driven axle. Thus, the gearbox is arranged between the driven and the undriven axle. Such axle arrangement is applicable both as front axles and as rear axles. The bogie arrangement or the arrangement with one driven and one undriven axle can be equipped with steerable or not steerable wheels and as a front or rear axle arrangement in the vehicle.
According to an advantageous sixth embodiment of the arrangement according to an aspect of the invention, at least one first power take off is arranged on said engine and at least one second power take off is arranged on said gearbox. An aspect of the invention makes it possible to have the power take offs nearer the power consumers.
According to an advantageous seventh embodiment of the arrangement according to an aspect of the invention said vehicle is a truck with an arrangement with parking brake function arranged in the vicinity of said rear axle and that said parking brake arrangement only acts on said rear wheels. Since, according to an aspect of the invention, the load over the front wheels decreases and the load over the rear wheels increases, it becomes possible to arrange a parking brake that is only acting on the rear wheels. The advantage is that the number of components in the truck can be minimized. No parking brake on the front wheels further decreases the load over the front axle.
According to an advantageous eight embodiment of the arrangement according to an aspect of the invention shafts of said gearbox are arranged substantially parallel to drive shafts of said driven axle. This enables the bevel gear to be placed on the low-torque input side of the gearbox. Thereby, the torque in the comparably expensive bevel gear is reduced significantly. Thus, this arrangement makes it possible to have a cost efficient bevel gear.
According to an another advantageous embodiment of the arrangement according to an aspect of the invention there is a bevel gear in each of said driven axles in a boggie arrangement. Said bevel gears are arranged in such a way compared to said driven axles that said bevel gears are substantially identical. The advantage is that identical bevel gear can be used for more than one driven axle.
According to another embodiment said bevel gears are connected to or integral with and driven by a common shaft, where said common shaft also can be a shaft in said multi-speed gearbox. Thus the number of components can be further rationalized.
According to an another advantageous embodiment of the arrangement according to an aspect of the invention said common shaft intersects a longitudinal median plane of the vehicle and a median plane between said driven rear axles in substantially the same point, so that said driven rear axles can be substantially identical. This embodiment makes it possible to have substantially both a first and a second bevel gears identical. And in the same arrangement both a first and a second entire driven rear axle identical.